Back at the end of 2014, I bought a cheap
Chinese Plasma Cutter, called a Giant Cut40 from a local
trader, at £185, it seemed to be a reasonable buy, the
trader was local in case of problems, so it was a
reasonable safe purchase.
By January 2015 I was decided it was project time and I
started to acquire parts to make a CNC frame for the
plasma, Nema 23 stepper motors, timing belts and pulleys
were purchased via Ebay along with a ball screw and a 4
channel controller. The software in use at the
time on a CNC milling machine was CNCPro an old DOS
The frame slowly started to take shape over the next few
months, I used 50 x 25 mm box section.
By this time it was June 2015, so I was six months into
the project and to be honest wondering why I was
At the end of June 2015, I thought the stage had been
reached to move the frame from the floor to a bench
position and apart from blowing controllers to useless
pieces dead electronics every now and then I managed to
achieve some good cuts. I use Qcad under Linux for
my drawing package and purchased a copy of Sheetcam to
translate across to Gcode.
The following video was June 2016 so still using the dos
program CNCPro But it toom me to this stage to stop the
controllers from failing on arc start. A home made
filter system of caps Zener diodes and MOV's between the
motors and the controller did the job for the most part.
One of the issues was cutting arc start up. To
this point I was dragging the plasma tip across the
metal, that was the only way to ensure the arc
started. But I knew I had to improve things, so
that meant investing time in better software such as
Mach3 even though Mach4 was coming out soon.
I looked at how I could get some form of pilot arc from
the cut 40 so I started to experiment, I did try it in
the early days with some success but for some reason
stopped, now was time to try again.
So I proved a system that would work and improved on it
in stages. It is worth note that in 2016 and 2017
I started to see Cut 50 Plasma cutters with a pilot arc
built in, Oh well!
The next stage was to probe the top of the work piece
for Zero height. If I had pilot arc I did not need
to drag the tip any more? So a micro-switch was
fitted to the 'floating head' design I was using, wired
into the probe input of mach3 and some macro code worked
out with help from the Mach3 forum and away I went.
It was now December 2016, 2 years from buying the Plasma
cutter and nearly two years into the project of CNC'ing
the unit. It has been suggested I should have
bought a Hypertherm, in fact I still get those comments,
perhaps when I can have a table bigger then the size of
a desk I may, but for now :)
The next stage of improvement was to add Torch height
Control, THC. Mach3 has a means of taking signals
from some basic units and moving the Z axis up or down
to suit, but prices were again not cheap and would cost
me more that the Plasma cutter cost in the first place,
so a sub project was started, please see a little
Filtering on the CNC Plasma
I have had a few comments about filtering, I guess that
as people start to build their own units, like me we
have issues with the HF start on the Chinese cut
So here is a circuit of the filter unit I added to the
output from the motor controller to the stepper
motors. The diagram only shows the output from one
motor/axis, so if you use 3 axis, you need 3
filters. This worked on mine, or shall I say
helped a lot, each machine set-up will be different, so
best experiment yourself and see what is best for your
Here is the Youtube video that accompanies the circuit.
A few repairs and a better camera!
June 2017 and I have just updated the table, for
the table it is a major update and potentially throws
all my previous cut setting out of the window! The
ball screw and number of steps per mm, meant the maximum
the table would run the Y axis at reliably was a maximum
speed of 1200 mm per minute. I would cut at 900 mm per
minute to make sure it did not miss steps.
So the Y axis was changed over to the same belt system
as X axis and I could go to a maximum speed of 7,000 mm
per minute. (275 ipm).
So new learning curve awaits as I figure out Amps
verses speed on my machine.
I have been playing again with settings and on
1.5mm steel cutting at 27 Amps at 2,200 mm/min.
Also a repair, or more like permanent fix of the Z
height probe switch as it kept moving!
So once I sorted that and added an aluminium shield to
protect the Y ways from the spash-back I had another go
I what I call a test piece. Apart from desperately
trying to pick out the tip-ups before they caught on the
head, this cut without any errors. total time was
something like 18 minutes 15 seconds.
Anyway this was my test piece for tonight, 450mm
I am saving my newer cutting
parameters and will update the table when I have
played a bit more.
The above mentioned Z Probe switch
meant I needed to remove the axis to sort, so I did a
couple of videos on my way of doing the Z zero
setting. details of mechanical switch,macros and
Here is a link to the M800 file as mentioned in the
Not updated for a while, here is a simple video, just to
show it is still here and working.
Just playing, it may give ideas for the festive season,
you can draw and cut similar items.
I had a few questions about the
Pilot arc system I used, so the best way I could
think of answering is with a video or two!
I find when the time comes to
change or get a new batch of consumables I have
issues, I have been finding the quality of fit,
manufacturing etc. to be different from one batch
to another. So I am trying a different style
torch, this being the SG-55. It is
physically bigger and meant for more amps
typically the 50 to 60 plus range, but I find you
can get 40 Amp consumables for it.
The above video is the first explanation and the
next one or possibly more will be about
use. First I have to make a mount to fit
the SG-55 to the Z-axis.
I eventually realised that
the handle part of the Sg-55A torch is 28mm
diameter and that is the same as some standard
plumbing fittings, so from the local hardware
store I picked up some plastic pipe clips the
sort that wrap all around the pipe. Took
the hole out to match a M6 screw thread and I
could mount directly to the from of the Z
axis. This made up for the extra weight
and then some as I could do without the steel
mount for the PT-31 torch. Wired in the
Pilot wire back to the resistors and ready for
it's first go:
The first go was very encouraging, so time
to make something else a simple 'key' holder
and time for a second go just to make sure
it was not a fluke:
So happy with the
new torch, seems to perform better, I
believe there should be less variance
in the parts, but time will tell, it
does mean I do not need the custom end
to provide Pilot arc so the air
passing the nozzle should be more
uniform and keep things a bit cooler,
perhaps helping shift the dross?
Next up, was to
help someone having difficulty with 1
mm aluminium, so a response in emails,
but thought I would see what gave me
good results when cutting 1 mm
aluminium. I went to 25 Amps at
5 metres per minute, just under 200
inch per minute, think I could go a
bit faster, but ran out of aluminium
for the time being.
So that brings the page up to date
for a little while.
Oh, I am
trying to cut sheet brass 1.6mm
thick, a simple clock. I
basically used same speeds as I
would for steel, but the cut edge
not as sharp, more dross, more of
a melted edge and it seems the
melted metal can solidify causing
a kerf/dross line on the edge of
the cut that is not as easy to